Hi Mohammed,
If you want to correct the document, then you simply need to reverse the GR and do the Standard Costing (CK11N or MR21) and then redo the GR.
If however correction to document is not required. then simply run Standard Costing and if the qty is in stock, it would generate price difference document and bring the stock valuations at par with Standard Price
Hope it helps
Regards
Mustafa Sakerwala